It is well documented that maintaining a correct tire pressure improves handling, increases gas mileage, and extends the useful life of vehicle tires. Moreover, while such factors are important to the owners of individual passenger vehicles, for fleets of commercial vehicles such as tractor trailers, trucks, buses, vans, and other types of commercial vehicles, such factors may have a significant effect on profitability, both in terms of energy consumption costs and tire replacement and/or retread costs.
Despite its irrefutable importance, tire pressure may not be monitored and maintained frequently enough by many fleets, as well as many in the overall driving public. In addition, with the advent of “extended mobility tires” (EMT) and their increasingly widespread commercial presence, it may be difficult for a vehicle operator to detect a low pressure or leak condition and take appropriate action. As a result, extended use of a tire in a low pressure condition beyond the manufacturer's recommended limit may occur.
Various legislative approaches requiring the communication of tire pressure information to the operator of a vehicle have been proposed, including a mandate that new vehicles be equipped with a low tire pressure monitoring system. Conventional tire pressure monitoring systems (TPMS's) typically incorporate a sensor located on each tire in a vehicle to perform real-time interior air pressure and temperature monitoring. The information is wirelessly transmitted to the driver via radio band frequencies (RF) and displayed in the driver compartment of the vehicle. The remote sensing module typically includes a pressure sensor, a temperature sensor, a signal processor, and an RF transmitter, and may be powered by a battery. Alternatively, a sensing module may be “passive”; that is, power may be supplied to the sensing module by way of magnetic coupling with a remote transmitter. The receiver may either be dedicated to tire pressure monitoring or share other functions in the vehicle. For instance the receiver controller may be the existing dashboard controller or the body controller. The receiver itself may further be shared with other systems using the same frequency range such as a remote keyless entry system.
The purpose of a tire monitoring system is to provide the driver with a warning should an anomaly occur in one or more tires. In some instances, tire pressure and/or temperature may be reported and/or displayed, while in other instances a simple low pressure alert may be generated. To be useful, the information must be quickly communicated and be reliable. However, displaying data derived from raw sensor measurements of temperature and pressure is not always sufficient to accurately represent the status of a tire at any given time and at various loads and conditions. The interpretation of measured data relating to temperature and pressure, therefore, is important, but has heretofore been problematic. Temperature and pressure readings by sensors in communication with a tire under conditions of actual use are influenced by various factors including heat emitted by the brakes; the thermal dissipation from the tire to the rim; load transfers that cause slight variations of the volume of the tires; and heat build-up in the tire due to its hysteretic losses. Such factors can affect the accuracy of information communicated to the driver, failing to alert the driver of marginal tire conditions under some circumstances and issuing false alarms to the driver in other instances.
Timeliness is also a concern with respect to conventional tire monitoring systems. Alerts to a driver of a low tire pressure condition may be based on simple thresholds, and once the driver is alerted due to the pressure falling below a threshold, the tire has already reached a non-optimal state. Leakages in a tire may be slow or fast, and particularly for faster leaks, the alert to the driver may be too late to enable the driver to rectify the situation without causing a tire failure or having to immediately stop the vehicle and change the tire or call for roadside assistance.
Consequently, a need exists in the art for processing information in a tire pressure monitoring system in an accurate and timely manner.
Furthermore, with respect to commercial vehicles, oftentimes the vehicles have more tires, travel greater distances, and thus a greater likelihood of tire failure, as well as typically a greater difficulty in resolving tire issues while in transit. For over-the-road tractor trailers, for example, the nearest service center may be tens of miles away and in many cases, a service vehicle will need to be dispatched to provide roadside assistance. In addition, from the perspective of a fleet, coordinating the service and maintenance of multiple fleet vehicles compounds these risks.
Therefore, a need also exists in the art for a tire monitoring system capable of reducing vehicle downtime, improving fuel economy, and reducing tire costs associated with fleets and the commercial vehicles used thereby.